1. Field of the Invention
The present invention relates to the detection of rotation angles, such as e.g. the rotation angle of a throttle flap of a throttle valve. In particular, the present invention relates to apparatus or sensors for detecting rotation angles operating on an analogue magnetic basis.
2. Description of Prior Art
Nowadays, the orientation of a rotary part as an absolute value and/or the rotation angle, which the rotary part includes with a fixed reference point, is often required for further processing, such as, for example, a feedback control or similar. These rotatable parts include both freely rotatable parts, such as, for example, axes and shafts of drives, and parts which are only rotatable in a partial area of the full circle, i.e. by less than 360xc2x0, such as, for example, rotary regulators or throttle flap valves. For measuring the rotation angle varying sensor systems or arrangements are currently known, which differ from each other both with respect to their accuracy, their reliability and their manufacturing cost. Basically, these sensor types may be organized into two different types, i.e. contact systems on the one hand and contactless systems on the other.
Contact systems are mostly based on a potentio-metric measurement and, due to their simple structure, characterize themselves by very low manufacturing costs. However, a great disadvantage of the contact systems consists in that high temperature drifts result in these systems and, when vibrations and oscillations occur, such as, for example, in a valve in a motor vehicle, even when the measuring system comprises a fixed rotary position, small movements of high frequencies may occur, which may result in a great wearout and in a premature failure of the system.
Contactless systems, in turn, can be subdivided into those of the analog and of the digital type. In contactless systems of the digital type, a more complex transducer is required, which logically subdivides the desired circle area, i.e. the area of possible rotation angles, into several partial segments. A known possibility includes, for example, a transducer structure in the form of a tooth gear or shaft gear which has a tooth missing at a certain position. Both the xe2x80x9cvacancyxe2x80x9d and the existing teeth may be detected by a suitable sensor technology operating on an optical or magnetic basis, with an angle position being detected by counting the teeth following the vacancy. Although only a transducer and a sensor are required for this, a disadvantage of this solution consists in that the determination of the angle may not be carried out until after the first pass or the first detection of the specifically marked position, i.e. of the missing tooth.
A further prior art realization of a contactless system of a digital type includes a complex transducer consisting of several transducer parts as well as one sensor each per transducer part. Each transducer part subdivides the desired circle area, i.e. the area of possible rotation angles, into various partial segments. The detection of the partial segments by the sensors may be carried out optically or magnetically, for example, via slot metal sheets. When suitably subdividing the desired circle areas, for example, by halving, quartering, etc. of the same, it may be achieved that the output signals of all sensors together indicate the value of the rotation angle in a digitally encoded form with a solution of one bit per sensor/transducer pair. For a resolution of approximately 1xc2x0, nine bits (512 possibilities) have to be encoded, and, as a consequence, nine transducer components and nine sensors are required for this purpose. On the basis of the suitable subdivision into partial segments, the signal is consequently available in digital form without any further A/C conversion. However, a disadvantage of these solutions consists in that an increase of the resolution may only be carried out by adding further transducer components and sensors. The higher the resolution to be achieved, the more complicated the required transducer is.
Conventionally, contactless analog systems operate with a simple magnet as a transducer and two analog magnetic-field sensors arranged to each other under 90xc2x0. Typically, magneto-resistive (MR) or Hall sensors are used. The transducer magnet is arranged such that its north/south axis runs in a radial direction, such that the magnetic-field sensors output signals of a sine and/or cosine course, from which the current rotation angle may be calculated. The resolution will be determined from the accuracy of the magnetic-field sensors, the environment influences and the conversion depth of the subsequent analog/digital conversion. Dependent on the arrangements of two sensors under exactly 90xc2x0, a great deal of labour and time is necessary for realizing this solution, making it relatively cost intensive.
On the basis of the technical conditions, contactless measurements are frequently necessary in many fields of applications and are of a considerable advantage. On the other hand, these contactless measurements are more complex and thus more expensive. For applications with an extremely high number of pieces, manufacturing costs for a rotation angle sensor play a very important role. Therefore, there is a need for a less complex contactlessly measuring rotation angle sensor.
In accordance with DE 3244891 C1, a system for detecting positions with linear motions is known, in which a simple magnet arranged in direction of the linear motion and a series of sensors arranged equidistantly and parallel to the linear motion, together defining a scale, are used. The sensors arranged in series detect the magnetic field, with the zero crossing of the vertical field component, which results from a central level through the magnet, being determined from the measurement, with the locus of the zero crossing indicating the locus of the magnet.
The object of the present invention consists in providing an apparatus for detecting a rotation angle of a rotation around an axis of rotation, which is less complex with comparable measuring qualities.
In accordance with the present invention this is achieved by an apparatus for detecting a rotation angle of a rotation around an axis of rotation, comprising a transducer magnet for generating a magnetic field and a plurality of magnetic-field-sensitive sensor elements for detecting the magnetic field, with the transducer magnet and the plurality of magnetic-field-sensitive sensor elements being arranged such that, when rotating around the axis of rotation, the plurality of magnetic-field-sensitive sensor elements circles around the same relative to the transducer magnet, and wherein the plurality of magnetic-field-sensitive sensor elements define a scale. The transducer magnet are arranged such that the generated magnetic field comprises a characteristic at a locus on the scale, and the locus on the scale uniquely depends on the rotary angle at least for a partial area of a full rotation. The transducer magnet is magnetized inclined to the axis of rotation.
The present invention is based on the recognition that the susceptibility of the potentio-metric systems, the complexity of contactless systems of the digital type with respect to the transducer structure, and the analog/digital conversion in the analog sine/cosine signal systems may be eliminated in that a transducer magnet and a scale defined by a plurality of magnetic-field-sensitive sensor elements which are arranged such to each other that the generated magnetic field comprises a characteristic at one location on the scale and that the locus on the scale uniquely depends at least for a partial area of a full rotation on the rotation angle. In this manner, it is on the one hand possible to use a simple transducer structure as is for example the case in the sine/cosine signal systems and to determine, and, on the other hand, to determine the rotation angle position from the measured magnetic-field data in a manner which is both simple and may be adapted to the desired resolution. In contrast to the above-mentioned contactless systems of the analog type, an inventive sensor and/or an inventive apparatus, for example, does not require any complex sine and cosine multiplier for evaluation, while, at the same time, as compared to the contactless systems of the digital type, the transducer structure may be clearly more simple.
The transducer magnet and the plurality of magnetic-field-sensitive sensor elements may be arranged such, that, when rotating around the axis of rotation, the plurality of magnetic-field-sensitive sensor elements circle around the same relative to the transducer magnet. Expressed differently, either the transducer magnet is fixedly arranged and the plurality of sensor elements are attached to the axis of rotation or the transducer magnet is attached to the axis of rotation and the plurality of sensor elements is fixedly arranged such that, when rotating around the axis of rotation, either the plurality of sensor elements circle around the transducer magnet or the transducer magnet rotates around the axis of rotation, while the plurality of sensor elements is fixedly arranged.
In one embodiment, the transducer magnet is magnetized inclined to or in an angular relationship to the axis of rotation. In this way the transducer magnet generates a magnetic field comprising a characteristic intersecting the scale defined by the plurality of sensor elements at a locus, which, in the case of rotations within at least one partial area of the full circle, uniquely depends on the rotation angle. In a special embodiment, the rotation angle area, for which the locus uniquely depends on the rotation angle, includes for example an area of 180xc2x0 or 90xc2x0.
A clear connection between the locus and the rotation angle in the full circle and/or within a rotation angle area spanning 360xc2x0, may be achieved, if this is not already the case by the generated magnetic field alone, in that, for example, a further signal is generated indicating a partial area of the rotation angle of a plurality of partial areas of a rotation angle, in which the rotation angle is currently located, or, expressed differently, which subdivides the rotation angle area into a plurality of partial areas of the rotation angle. By receiving the signal indicating the partial area of the rotation angle, clear inferences can be made as regards the rotation angle from a combination from this signal and the locus on the scale within the total full circle.
A further possibility for extending the rotation angle area with a unique assignment between the rotation angle and the locus of the magnetic-field characteristic consists in duplicating the plurality of sensor elements such that a second plurality of sensor elements with the same function is offset relative to the first plurality of sensor elements by a rotation around the axis of rotation. In this case, a combination of the loci on the first scale and a second scale, which is defined by the second plurality of sensor elements, in which the generated magnetic field comprises the characteristic, uniquely depends on the rotation angle within the total full circle.
The sensor elements may be arranged on a level which is spaced from the axis of rotation and which is parallel to the same, such that an integration of the sensor elements into a die, such as for example in the form of Hall sensors, is possible. In a special embodiment, the sensor elements are arranged in the form of a two-dimensional or one-dimensional array. A preferred arrangement of the sensor elements includes a linear arrangement of the same in parallel to the axis of rotation.
The characteristic comprising the generated magnetic field at the locus on the scale defined by the sensor elements may be a zero crossing, a relative minimum or a relative maximum of a component of the magnetic field in any predetermined direction or the amount of the magnetic field. The loci, at which the magnetic field comprises the characteristic, form a geometric extension rotating around the axis of rotation relative to the sensor elements during a rotation around the axis of rotation. Within a rotation angle area to be detected, the geometric extension intersects the scale defined by the sensor elements at a certain locus. This locus of the magnetic-field characteristic on the scale uniquely depends on the rotation angle within the rotation angle area to be detected. The locus may be determined from the magnetic-field data of the sensor elements, for example, by means of interpolation, while, within the rotation angle area to be detected, a clear inference may be made from the locus on the rotation angle. In accordance with a special embodiment, the previously mentioned characteristic of the magnetic-field includes, for example, the zero crossing of the radial component of the magnetic field, with the loci, at which the magnetic field comprises this characteristic, forming an essentially vertical surface to a magnetization direction of the transducer magnet.
In contrast to conventional sensor systems, an inventive sensor is especially advantageous in that the sensor part is adapted to be integrated into a single die, which, for example, may be manufactured in a CMOS standard technology, thereby maintaining manufacturing costs at a low level. In addition, the transducer magnet may be manufactured in a much simpler and inexpensive manner than is the case with digital angle position transducer. A high degree of accuracy may be achieved without any extremely high resolving analog/digital converters being necessary. In addition, the orientation information and/or the detected rotation angle are immediately available, for example immediately after turning on the sensor, other than is the case in the previously described contactless sensor system of the digital type having the missing gear.